1. Field of the Invention
This invention relates to a radiation image read-out method and apparatus for obtaining an image signal which represents a radiation image, from a solid-state radiation detector, which converts incident radiation into an electric signal. This invention also relates to a solid-state radiation detector for use in the radiation image read-out method and apparatus.
2. Description of the Prior Art
Radiation image recording and read-out apparatuses utilizing radiation film or stimulable phosphor sheets have heretofore been used widely for obtaining radiation images for medical diagnosis, or the like.
Also, recently, various radiation image recording and read-out apparatuses utilizing solid-state radiation detectors (comprising semiconductors as major parts), which detect radiation and feed out image signals, have been proposed and have widely been used in practice. As the solid-state radiation detectors utilized in the radiation image recording and read-out apparatuses, various types of solid-state radiation detectors have been proposed. Typical examples of the solid-state radiation detectors include photo conversion types or direct conversion types of solid-state radiation detectors, in which accumulated electric charges (also referred to as the latent image charges) carrying image information are detected with thin-film transistors (TFT""s), and improved direct conversion types of solid-state radiation detectors, in which the latent image charges carrying image information are detected by scanning with reading light.
The photo conversion types of solid-state radiation detectors comprise solid-state detection means (two-dimensional image read-out means) and a fluorescent material overlaid upon the solid-state detection means. The solid-state detection means comprises an insulating substrate and a plurality of photoelectric conversion devices, which are formed in a two-dimensional pattern on the insulating substrate and which are provided with charge accumulating sections for accumulating electric charges. When the fluorescent material is exposed to radiation carrying image information, it converts the radiation into the fluorescence. The fluorescence is detected, and the thus obtained electric charges are accumulated at the charge accumulating sections of the photoelectric conversion devices. The TFT""s, each of which is connected to one of the photoelectric conversion devices, are operated successively, and the accumulated charges are thereby converted into a radiation image signal and fed out. The photo conversion types of solid-state radiation detectors are described in, for example, Japanese Unexamined Patent Publication Nos. 59(1984)-211263 and 2(1990)-164067, PCT International Publication No. WO92/06501, and SPIE Vol. 1443, Medical Imaging V; Image Physics (1991), pp. 108-119.
The direct conversion types of solid-state radiation detectors comprise solid-state detection means and a radio-conductive material overlaid upon the solid-state detection means. The solid-state detection means comprises an insulating substrate and a plurality of charge collecting electrodes, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to one pixel. When the radio-conductive material is exposed to radiation carrying image information, it generates electric charges carrying the image information. The direct conversion types of solid-state radiation detectors are described in, for example, xe2x80x9cMaterial Parameters in Thick Hydrogenated Amorphous Silicon Radiation Detectors,xe2x80x9d Lawrence Berkeley Laboratory, University of California, Berkeley, Calif. 94720 Xerox Parc. Palo Alto. Calif. 94304; xe2x80x9cMetal/Amorphous Silicon Multilayer Radiation Detectors, IEE TRANSACTIONS ON NUCLEAR SCIENCE, Vol. 36, No. 2, April 1989; and Japanese Unexamined Patent Publication No. 1(1989)-216290. In the direct conversion types of solid-state radiation detectors, solid-state detecting devices comprise the charge collecting electrodes and the radio-conductive material as the major parts. When the accumulated charges carrying the radiation image information are to be. detected as an image signal from the direct conversion types of solid-state radiation detectors, as in the aforesaid photo conversion types of solid-state radiation detectors, the solid-state detecting devices are scanned with the TFT""s, each of which is connected to one of the solid-state detecting devices.
The improved direct conversion types of solid-state radiation detectors have been proposed by the applicant in Japanese Patent Application No. 10(1998)-232824. The improved direct conversion types of solid-state radiation detectors are improved over the direct conversion types of solid-state radiation detectors and utilize a photo reading technique for performing the reading operation by the scanning with reading light. The improved direct conversion types of solid-state radiation detectors comprise:
i) a first electrical conductor layer having permeability to recording radiation,
ii) a recording photo-conductive layer, which exhibits photo-conductivity (in the strict sense, radio-conductivity) when it is exposed to the recording radiation having passed through the first electrical conductor layer,
iii) a charge transporting layer, which acts approximately as an insulator with respect to electric charges having a polarity identical with the polarity of electric charges occurring in the first electrical conductor layer, and which acts approximately as a conductor with respect to electric charges having a polarity opposite to the polarity of the electric charges occurring in the first electrical conductor layer,
iv) a reading photo-conductive layer, which exhibits photo-conductivity (in the strict sense, electromagnetic wave conductivity) when it is exposed to a reading electromagnetic wave, and
v) a second electrical conductor layer having permeability to the reading electromagnetic wave,
the layers being overlaid in this order. In the improved direct conversion types of solid-state radiation detectors, latent image charges carrying image information are accumulated at an interface between the recording photo-conductive layer and the charge transporting layer. The first electrical conductor layer and the second electrical conductor layer act as electrodes. Also, in the improved direct conversion types of solid-state radiation detectors, solid-state detecting devices comprise the recording photo-conductive layer, the charge transporting layer, and the reading photo-conductive layer as the major parts.
In the improved direct conversion types of solid-state radiation detectors, the reading of the latent image charges (i.e., the reading of the electrostatic latent image represented by the latent image charges) may be performed with a technique, wherein the second electrical conductor layer (i.e., a reading electrode) is constituted of a flat plate-shaped electrode, and the reading electrode is scanned with spot-like reading light, such as a laser beam, the latent image charges being thereby detected. Alternatively, the latent image charges may be read with a technique, wherein the reading electrode is constituted of comb tooth-shaped electrodes (i.e., stripe-shaped electrodes), and the stripe-shaped electrodes are scanned with light, which is produced by a line light source extending along a direction approximately normal to the longitudinal direction of each stripe-shaped electrode, the scanning with the light being performed in the longitudinal direction of each stripe-shaped electrode. In this manner, the latent image charges are detected. In cases where either one of the reading techniques is employed, the solid-state radiation detector is formed as a two-dimensional solid-state radiation detector constituted of a plurality of solid-state detecting devices, which are arrayed in a substantially matrix-like form and each of which corresponds to one pixel. Specifically, as for the solid-state radiation detector itself, it cannot be said that the individual solid-state detecting devices are arrayed in a matrix-like form. However, in the step of processing the image signal obtained by reading the latent image charges, for example, a signal component at a sampling point can be regarded as a signal component representing a predetermined pixel. Therefore, the solid-state detecting devices are referred to as being arrayed in a xe2x80x9csubstantiallyxe2x80x9d matrix-like form. In cases where the reading electrode is constituted of the stripe-shaped electrodes, with respect to the direction in which the stripe-shaped electrodes stand side by side, each stripe-shaped electrode itself corresponds to a pixel.
Each of the various types of solid-state radiation detectors described above comprises a plurality of solid-state detecting devices for converting radiation into an electric signal, which are arrayed in a matrix-like form. Each type of solid-state radiation detector described above feeds out an image signal, which represents a radiation image, as two-dimensional matrix information.
In cases where radiation images are read out by utilizing the solid-state radiation detectors, the solid-state radiation detectors of various different image sizes are often utilized in accordance with the portion of an object the image of which is recorded, the image recording mode used, and the like.
Alteration of the image size is ordinarily performed by changing the total number of the solid-state detecting devices constituting the solid-state radiation detector, while the size of the detection region per pixel (hereinbelow referred to as the pixel size), which is determined by the array pitch of the solid-state detecting devices, and the like, being kept unchanged, i.e. while the read-out density (the pixel density) of the solid-state radiation detector being kept unchanged. Specifically, the image size is altered by setting how many solid-state detecting devices of an identical pixel size are arrayed. Therefore, the total number of pixels varies for different image sizes. Also, in accordance with the variation of the total number of pixels, the total number of pixels, which are read out, varies.
Ordinarily, in output apparatuses, such as printers and monitors, for reproducing (outputting) visible radiation images in accordance with read-out image signals, which have been obtained from the solid-state radiation detectors, and image filing apparatuses for filing the radiation images (both apparatuses will hereinbelow be referred to as the radiation image read-out apparatuses), the number of pixels in each of the reproduced images or the filed images is fixed at a predetermined value or is variable only in a narrow range.
Therefore, in cases where read-out processing is performed with respect to solid-state radiation detectors of different image sizes, for example, while the read-out densities of the solid-state radiation detectors are being unchanged, it becomes necessary for the read-out image signals having been obtained from the solid-state radiation detectors to be processed such that, as the image size of the solid-state radiation detector becomes large, the pixel density may be set to be low. In this manner, regardless of the image sizes of the solid-state radiation detectors, the number of pixels in each of the reproduced images or the filed images must be set at a predetermined value or approximately at the predetermined value, and the image sizes of the reproduced images or the filed images must thereby be set approximately at a predetermined size. Thus it becomes necessary for the number of pixels in the image, which is represented by the read-out image signal having been obtained from the solid-state radiation detector, to be altered in accordance with the image size, which is required from the aspect of image reproduction or image filing.
Also, in a built-in type of radiation image recording and read-out apparatus having a solid-state radiation detector fixedly, a solid-state radiation detector for the maximum image size is ordinarily built in the radiation image recording and read-out apparatus. With the built-in type of radiation image recording and read-out apparatus, in cases where an operation for recording an image of an image size smaller than the maximum image size is performed, only the image signal corresponding to the region within the specified read-out image size is processed as an effective image signal. Such a technique is referred to as the logical readout. In cases where the logical readout is performed, as in the cases described above, it becomes necessary for the number of pixels in the image, which is represented by the read-out image signal having been obtained from the solid-state radiation detector, to be altered in accordance with the image size, which is required,from the aspect of image reproduction or image filing.
The primary object of the present invention is to provide a radiation image read-out method in which, in cases where read-out processing is performed with respect to different image sizes, a read-out density of a solid-state radiation detector need not be altered but which is capable of coping with narrowness of an allowable width of a number of pixels in an image reproducing apparatus or an image filing apparatus.
Another object of the present invention is to provide an apparatus for carrying out the radiation image read-out method.
The specific object of the present invention is to provide a solid-state radiation detector for use in the radiation image read-out method and apparatus.
The present invention provides a radiation image read-out method, comprising the steps of obtaining an image signal, which represents a radiation image, from a solid-state radiation detector constituted of a plurality of solid-state detecting devices for detecting radiation, which are arrayed in a matrix-like form along a main scanning direction and a sub-scanning direction and each of which corresponds to one pixel,
wherein the improvement comprises the step of performing a pixel density transforming process on the image signal and in accordance with a pixel size, which is determined in accordance with a desired image size.
In the radiation image read-out method in accordance with the present invention, the pixel density transforming process should preferably be performed in accordance with a pixel density of an output apparatus, such as a printer, which receives an image signal having been obtained from the pixel density transforming process. For example, in cases where a pixel size of each of the solid-state detecting devices falls within the range of 100 xcexcm to 200 xcexcm, the pixel density transforming process should preferably be performed such that a pixel size in an image outputted from the output apparatus falls within the range of 40 xcexcm to 100 xcexcm. In such cases, the pixel density transforming process should more preferably be performed such that the pixel size in the image outputted from the output apparatus falls within the range of 70 xcexcm to 90 xcexcm. As in the correspondence relationship between the pixel size of each of the solid-state detecting devices of the solid-state radiation detector, the pixel density of the output apparatus and the pixel size in the image outputted from the output apparatus have the correspondence relationship such that, if one of the pixel density and the pixel size is determined, the other of the pixel density and the pixel size will be determined.
The radiation image read-out method in accordance with the present invention should preferably be modified such that, as an effective image size of the solid-state radiation detector becomes large, a magnification ratio of pixel density transformation in the pixel density transforming process is set to be low with respect to each of a row direction and a column direction.
Also, the radiation image read-out method in accordance with the present invention should preferably be modified such that the pixel density transforming process is performed such that, with respect to each of a row direction and a column direction, a magnification ratio of pixel density transformation is equal to n/m, where n represents a positive integral number and m represents a positive integral number equal to at most a number of pixels of the solid-state detecting devices along the main scanning direction or the sub-scanning direction. The term xe2x80x9cnumber of pixels of solid-state detecting devices along a main scanning direction or a sub-scanning directionxe2x80x9d as used herein means the total number of pixels along each of the main scanning direction and the sub-scanning direction of the effective image size of the solid-state radiation detector. The main scanning direction may be taken as the row direction, and the sub-scanning direction may be taken as the column direction. Alternatively, the main scanning direction may be taken as the column direction, and the sub-scanning direction may be taken as the row direction. Also, the magnification ratio of pixel density transformation with respect to the row direction and the magnification ratio of pixel density transformation with respect to the column direction may be identical with each other or may be different from each other.
Further, in the radiation image read-out method in accordance with the present invention, the pixel density transforming process may be performed by multiplying each of image signal components, which are fed out from the solid-state detecting devices corresponding to a pixel of interest and the neighboring pixels, by a predetermined coefficient, and thereafter adding values of products obtained from the multiplication. The term xe2x80x9cpixel of interestxe2x80x9d as used herein means the pixel, which includes the position of the pixel obtained from the pixel density transforming process, or the pixel, which is closest to the position of the pixel obtained from the pixel density transforming process.
The present invention also provides an apparatus for carrying out the radiation image read-out method in accordance with the present invention. Specifically, the present invention also provides a radiation image read-out apparatus, comprising means for obtaining an image signal, which represents a radiation image, from a solid-state radiation detector constituted of a plurality of solid-state detecting devices for detecting radiation, which are arrayed in a matrix-like form along a main scanning direction and a sub-scanning direction and each of which corresponds to one pixel,
wherein the improvement comprises the provision of pixel density transforming means for performing a pixel density transforming process on the image signal and in accordance with a pixel size, which is determined in accordance with a desired image size.
In the radiation image read-out apparatus in accordance with the present invention, the pixel density transforming means should preferably perform the pixel density transforming process in accordance with a pixel density of an output apparatus, which receives an image signal having been obtained from the pixel density transforming process. For example, in cases where a pixel size of each of the solid-state detecting devices falls within the range of 100 xcexcm to 200 xcexcm, the pixel density transforming means should preferably perform the pixel density transforming process such that a pixel size in an image outputted from the output apparatus falls within the range of 40 xcexcm to 100 xcexcm. In such cases, the pixel density transforming means should more preferably perform the pixel density transforming process such that the pixel size in the image outputted from the output apparatus falls within the range of 70 xcexcm to 90 xcexcm.
In the radiation image read-out apparatus in accordance with the present invention, the pixel density transforming means should preferably operate such that, as an effective image size of the solid-state radiation detector becomes large, a magnification ratio of pixel density transformation in the pixel density transforming process is set to be low (i.e., the pixel density is set to be low) with respect to each of a row direction and a column direction.
Also, in the radiation image read-out apparatus in accordance with the present invention, the pixel density transforming means should preferably perform the pixel density transforming process such that, with respect to each of a row direction and a column direction, a magnification ratio of pixel density transformation is equal to n/m, where n represents a positive integral number and m represents a positive integral number equal to at most a number of pixels of the solid-state detecting devices along the main scanning direction or the sub-scanning direction.
Further, in the radiation image read-out apparatus in accordance with the present invention, the pixel density transforming means may perform the pixel density transforming process by multiplying each of image signal components, which are fed out from the solid-state detecting devices corresponding to a pixel of interest and the neighboring pixels, by a predetermined coefficient, and thereafter adding values of products obtained from the multiplication. The image signal components, which are fed out from the solid-state detecting devices, should preferably be of analog values.
The present invention further provides a solid-state radiation detector, comprising a plurality of solid-state detecting devices for detection of radiation, which are: arrayed in a matrix-like form and each of which corresponds to one pixel, and having read-out functions for feeding out a detection signal, which has been detected by the solid-state detecting devices, as an image signal, wherein the improvement comprises the provision of pixel density transforming means for performing a pixel density transforming process on the image signal and in accordance with a pixel size, which is determined in accordance with a desired image size.
In the solid-state radiation detector in accordance with the present invention, as in the aforesaid radiation image read-out method and apparatus in accordance with the present invention, the pixel density transforming means should preferably operate such that, as an effective image size of the solid-state radiation detector becomes large, a magnification ratio of pixel density transformation in the pixel density transforming process is set to be low with respect to each of a row direction and a column direction.
Also, in the solid-state radiation detector in accordance with the present invention, the pixel density transforming means should preferably perform the pixel density transforming process such that, with respect to each of a row direction and a column direction, a magnification ratio of pixel density transformation is equal to n/m, where n represents a positive integral number and m represents a positive integral number equal to at most a number of pixels of the solid-state detecting devices along the main scanning direction or the sub-scanning direction.
Further, in the solid-state radiation detector in accordance with the present invention, the pixel density transforming means may perform the pixel density transforming process by multiplying each of image signal components, which are fed out from the solid-state detecting devices corresponding to a pixel of interest and the neighboring pixels, by a predetermined coefficient, and thereafter adding values of products obtained from the multiplication. In such cases, the image signal components, which are fed out from the solid-state detecting devices, should preferably be of analog values.
In the radiation image read-out method and apparatus and the solid-state radiation detector in accordance with the present invention, the solid-state radiation detector may be one of various types of solid-state radiation detectors comprising a plurality of solid-state detecting devices for conversion of radiation into an electric signal, which are arrayed in the matrix-like form, and feeding out an image signal, which represents a radiation image. Typical examples of the solid-state radiation detectors include the photo conversion types of solid-state radiation detectors, the direct conversion types of solid-state radiation detectors, and the improved direct conversion types of solid-state radiation detectors, which will be described later. However, the solid-state radiation detector is not limited to these types of solid-state radiation detectors.
As will be described later, in the cases of the improved direct conversion types of solid-state radiation detectors, as for the solid-state radiation detector itself, it cannot be the that the individual solid-state detecting devices are arrayed in a matrix-like form. However, in the step of processing the detected image signal, for example, a signal component at a sampling point can be regarded as a signal component representing a predetermined pixel. Therefore, it can be regarded that the solid-state detecting devices are arrayed in a substantially matrix-like form so as to correspond to the pixels. The solid-state radiation detector employed in the radiation image read-out method and apparatus in accordance with the present invention may be the one, in which the individual solid-state detecting devices are arrayed in an exactly matrix-like form, or the one, in which the individual solid-state detecting devices are arrayed in a substantially matrix-like form.
The term xe2x80x9cdesired image sizexe2x80x9d as used herein means the image size, which is determined by the pixel density and the pixel size and which is required in cases where an image is outputted from a printer, or the like, by the utilization of the image signal obtained from the solid-state radiation detector or in cases where the image signal is stored in a filing apparatus.
The term xe2x80x9cpixel density transforming processxe2x80x9d as used herein means the process performed on the image signal made up of a series of image signal components, which have been fed out from the solid-state detecting devices corresponding to pixels, for obtaining an image signal made up of a series of image signal components, which represent pixels of a size different from the pixel size determined by the solid-state detecting devices themselves, and thereby altering the pixel density of the image signal having been fed out from the solid-state radiation detector. The pixel density transforming process embraces a pixel density lowering process, in which the pixel density is set to be low by enlarging the pixel size, and a pixel density raising process, in which the pixel density is set to be high by reducing the pixel size. The term xe2x80x9cpixel size determined by solid-state detecting devices themselvesxe2x80x9d as used herein means the size of the detection region per pixel, which is determined by the array pitch of the solid-state detecting devices, and the like.
The term xe2x80x9cpixel density lowering processxe2x80x9d as used herein means the process for obtaining a new image signal made up of a series of image signal components, which represent pixels of a size larger than the pixel size determined by the solid-state detecting devices themselves, and thereby setting the pixel density to be low. By way of example, with the pixel density lowering process, a plurality of image signal components, which have been fed out from the solid-state detecting devices corresponding to a plurality of pixels adjacent to one another, may be mixed together, and the resulting image signal component may be employed as an image signal component representing a new pixel.
The term xe2x80x9cpixel density raising processxe2x80x9d as used herein means the process for obtaining a new image signal made up of a series of image signal components, which represent pixels of a size smaller than the pixel size determined by the solid-state detecting devices themselves, and thereby setting the pixel density to be high. By way of example, with the pixel density raising process, processing may be performed on a plurality of image signal components, which have been fed out from the solid-state detecting devices corresponding to a plurality of pixels adjacent to one another, and an image signal component representing a new pixel, which is located among the plurality of the pixels adjacent to one another, may thereby be obtained.
In the pixel density lowering process and the pixel density raising process, the image signal components corresponding to the plurality of the pixels may be weighted, and the new image signal component may be obtained from the weighted image signal components. In such cases, weight factors employed in the weighting may be set in one of various manners. For example, weight factors of an identical value may be employed for the image signal components corresponding to all of the pixels (as in simple mean calculations). Alternatively, weight factors of different values may be employed for the image signal components corresponding to different pixels (as in weighted mean calculations). Also, one of various known interpolation processing techniques, such as a nearest neighbor interpolation technique, a polynomial interpolation technique, a Lagrangean interpolation technique, a spline interpolation technique, and a combination of two or more of the above-enumerated interpolation techniques, may be employed.
The solid-state radiation detector employed in the radiation image read-out method and apparatus in accordance with the present invention is not limited to the three types of solid-state radiation detectors described above. The solid-state radiation detector may be one of various other types of solid-state radiation detectors, which have semiconductors as the major parts and are constituted of a plurality of arrayed solid-state detecting devices for detecting radiation.
With the radiation image read-out method and apparatus in accordance with the present invention, the pixel density transforming process is performed on the image signal and in accordance with the pixel size, which is determined in accordance with a desired image size. Therefore, the number of pixels in the image processed in image processing at the post stage can be set at a desired value (i.e., the image size of the image reproduced or outputted can be set approximately at a predetermined size) regardless of the effective image size of the solid-state radiation detector. For example, as the effective image size of the solid-state radiation detector becomes large, the magnification ratio of pixel density transformation in the pixel density transforming process may be set to be low with respect to each of the row direction and the column direction. In this manner, the number of pixels in the image processed in the image processing at the post stage can be set at a predetermined value or approximately at the predetermined value. Accordingly, a single image reproducing apparatus or a single image filing apparatus can be utilized for a plurality of solid-state radiation detectors of different image sizes and for a plurality of read-out image sizes varying in the logical readout.
Also, with the radiation image read-out method and apparatus in accordance with the present invention, wherein the pixel density transforming process is performed in accordance with the pixel density of the output apparatus, such as a printer, the effects described below can be obtained. Specifically, the pixel size of each of the solid-state detecting devices constituting the solid-state radiation detector can be set in accordance with the detection signal quantity (i.e., the signal-to-noise ratio) of each solid-state detecting device. Also, in the output apparatus, such as a printer, for outputting the image in accordance with the image signal having been obtained from the solid-state radiation detector, the pixel size can be set such that recording (output) scanning lines may become imperceptible. Further, the difference between the pixel size of each solid-state detecting device and the pixel size of the output apparatus can be compensated for by performing the pixel density transforming process. Therefore, in the solid-state radiation detector, the pixel size can be set at an appropriate size regardless of the image size (the pixel size) of the output apparatus. Also, in the output apparatus, the pixel size can be set at an appropriate size regardless of the image size (the pixel size) of the solid-state radiation detector.
Further, with the radiation image read-out method and apparatus in accordance with the present invention, wherein the pixel density transforming process is performed such that, with respect to each of the row direction and the column direction, the magnification ratio of pixel density transformation is equal to n/m, where n represents appositive integral number and m represents a positive integral number equal to at most a number of pixels of the solid-state detecting devices along the main scanning direction or the sub-scanning direction, the weighted operations and the interpolating operations can be performed with simple operation process. Particularly, the pixel density transforming process performed in this manner is suitable for digital signal processing. Also, since m is a positive integral number equal to at most a number of pixels of the solid-state detecting devices along the main scanning direction or the sub-scanning direction, with respect to an approximately entire image area other than the peripheral regions of the effective image size, the weighted operations and the interpolating operations can be performed by utilizing the image signal components having been obtained from the solid-state detecting devices.
Furthermore, with the radiation image read-out method and apparatus in accordance with the present invention, the pixel density transforming process may be performed by multiplying each of the image signal components, which are fed out from the solid-state detecting devices corresponding to the pixel of interest and the neighboring pixels, by a predetermined coefficient, and thereafter adding the values of products obtained from the multiplication. In such cases, the pixel density transforming process can be performed with the so-called filtering process. Particularly, the, pixel density transforming process performed in this manner is suitable for analog signal processing.
With the solid-state radiation detector in accordance with the present invention, which is provided with the pixel density transforming means for performing the pixel density transforming process described above, an integral type of solid-state radiation detector having the pixel density transforming functions can be obtained.